Long term evolution (“LTE”), also referred to as 3.9G, refers to research and development involving the third generation partnership project (“3GPP”), which is the name generally used to describe an ongoing effort across the industry aimed at identifying technologies and capabilities that can improve systems such as the universal mobile communication system (“UMTS”). The goals of this broadly based project include improving communication efficiency, lowering costs, improving services, making use of new spectrum opportunities, and achieving better integration with other open standards. The 3GPP LTE project is not itself a standard-generating effort, but will result in new recommendations for standards for the UMTS.
The evolved universal terrestrial radio access network (“E-UTRAN”) in 3GPP includes base stations, providing user plane (including packet data convergence protocol/radio link control/medium access control/physical sublayers) and control plane (including a radio resource control sublayer) protocol terminations towards mobile terminal devices. A mobile terminal device such as a wireless mobile terminal device is generally known as a user equipment (“UE”). A base station is an entity of a communication network often referred to as a Node B or an NB. Particularly in the E-UTRAN, a base station is referred to as an eNB. The base stations are interconnected with each other by X2 interfaces. The base stations are also connected by S1 interfaces to an evolved packet core. For details about the overall architecture of the E-UTRAN, see 3GPP TS 36.300, v1.0.0 (2007-03), which is incorporated herein by reference.
As communication systems such as cellular telephone, satellite, and microwave communication systems become widely deployed and continue to attract a growing number of users, there is a pressing need to accommodate a large and variable number of communication devices transmitting a growing volume of data with fixed resources. Traditional communication system designs employing a fixed resource (e.g., a fixed data rate for each communication device) have become challenged to provide high, but flexible, data transmission rates in view of the rapidly growing customer base and expanding levels of service.
To dynamically allocate uplink (“UL”) and downlink (“DL”) data packet transmission resources among all the user equipment connecting to the base station, a base station includes one or more packet schedulers controlled by the radio resource control (“RRC”) sublayer. The packet scheduler takes into account the traffic volume and the quality of service (“QoS”) requirements of each user equipment and associated radio bearers, assigns resources among user equipments, and possibly also between different radio bearers associated with a single user equipment.
For uplink transmission, in principle, the user equipments are only allowed to transmit data at their allocated time intervals. If there is data to be transmitted, a user equipment temporarily stores the data in a buffer and transmits the data using available uplink resource allocations. In order to obtain the uplink resource allocations, the user equipment needs to indicate a request to the base station by providing measurement reports. The measurement reports may include buffer status reports and measurements of the radio environment of the user equipment. The packet scheduler of the base station schedules uplink resource allocations according to the measurement reports.
The user equipments in the UMTS, for instance, are operated in various RRC modes such as connected, idle, etc. In the LTE, these RRC modes are simplified into three modes, namely, LTE_Active, LTE_Idle and LTE_Detached. In the active mode (e.g., LTE_Active), the user equipment has an active connection to the base station for transmitting and receiving signals. If the buffer of the user equipment is empty and there is no incoming data to be transmitted, the user equipment enters a discontinuous reception (“DRX”) state. The discontinuous reception state is characterized by a discontinuous reception period (using a discontinuous reception timer), which may be variable in length. The length of the discontinuous reception period may depend on the connection requirements of the current connection(s), and may vary between zero seconds (no discontinuous reception applied, also referred to as non-discontinuous reception mode) to a relatively long period (e.g., up to 5.12 seconds). In the discontinuous reception period, the user equipment listens on one or more of a physical downlink control channel (“PDCCH”) at each discontinuous reception timeout to see if any allocations are reserved therefor. The purpose for using the discontinuous reception is to prolong battery life of the user equipment.
The user equipments may request uplink resource allocations for future use. Scheduling requests for future allocations are sent in the same way as uplink data transmissions (e.g., via shared transport channels or via dedicated control signaling in the uplink). Since the allocation of resources is based on buffer status reports, if a user equipment's buffer is empty, the base station packet scheduler may not schedule any resource to the user equipment, even for transmitting a request. Therefore, the user equipment may have to send the request by using a different channel, for example, by using a random access channel (“RACH”) or a packet uplink control channel (“PUCCH”). The RACH procedure is a standard procedure for requesting uplink resources in other communication systems as well as in the LTE or an RRC idle and/or detached mode. The RACH procedure may also be used in LTE_Active (RRC_connected) mode for requesting resources in the uplink. Sending scheduling requests on the PUCCH is applicable to user equipment in an RRC_connected mode and with valid uplink timing advance.
A problem may occur when the user equipment receives new uplink data for transmission after being without any uplink resource allocation for a period of time. The user equipment does not know if and when the communication system may allocate uplink resources to the user equipment. If the user equipment waits until the next uplink resource allocation to transmit the data, it might have to wait for a long time, which may not be acceptable for the user of the user equipment or the communication system. For example, if the user equipment has to transfer data on a radio bearer that has strict timing requirements, under the current scheme, the transmission might not be initiated quickly enough. On the other hand, if the user equipment already has allocations scheduled for future use (e.g., if persistent uplink/downlink resource allocations already exist), initiating a RACH procedure for requesting uplink resources would be unnecessary and wasteful, since it consumes communication system resources.
Another problem of the RACH procedure is related to the RACH reply from the base station to the user equipment. It may be possible that even though the user equipment requests resource allocations using the RACH, the network cannot or will not assign resources to the user equipment. This leaves the RACH request “unanswered.” The communication system not answering or replying the RACH request might have negative side effects on the user equipment. On the other hand, the base station may wish to schedule the user equipment, but the scheduling will be assigned at a next timed resource allocation at the end of a discontinuous reception period. If so, the user equipment needs to be informed.
Therefore, what is needed in the art is a system and method that allows for more flexible or efficient scheduling of uplink resources, especially, when the user equipment enters or is in the active mode. Accordingly, what is also needed is a user equipment equipped for performing a procedure for flexible or efficient scheduling of uplink resources, and a communication system entity such as a base station that facilitates the execution of the procedure and assigns the uplink transmission resources according thereto.